This application claims priority of DE 198 51 745.9, filed Nov. 10, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a transfer system, particularly for the transfer of workpieces between successive machining stations, such as press stages of large-piece transfer presses.
As a rule, a transfer system, which extends along the entire length of the press and moves the individual workpieces in synchronism, carries out the piece transport from one press stage to another. Such a known transfer system is described, for example, in DE 41 43 099 A1. This transfer system has two transfer rails which extend along the length of the press and on which carriages are disposed. Two carriages respectively carry a cross traverse between one another which is provided with suction spiders for receiving workpieces. For carrying out the transfer step from one press stage to another, the carriages are connected by a linkage with a cam drive which is connected with the main drive of the press. A lifting and lowering movement is superimposed on the back-and-forth movement of the transfer rails achieved in this manner. This lifting and lowering movement is achieved in that the rails are lifted and lowered as a whole.
Such a transfer system synchronously moves the suction traverses connected with a cam drive. Correspondingly, the participating tools must open and close simultaneously.
In contrast, WO 93/00185, discloses a transfer system which has transfer modules between individual press stages. The transfer modules can be controlled independently of one another. Each transfer module has two driving units which are applied on the right and the left to a respective suction traverse. The driving units contain a lifting unit, which is stationarily disposed, and an advancing unit, which is lifted and lowered by the lifting unit. The advancing unit contains a motor which drives the suction bridge by way of a planetary gear combined with a double crank. In this case, the backlash of the planetary gear is added to a possible bearing play between the individual interlinked cranks which finally adds up to an unreliable positioning existing at the suction bridge.